The use of cavity die molds has progressed from the use of single cavity dies, through multi-cavity dies; the use of 2-level synchronized stacked mold arrangements, to the use of 4-level desynchronized stacked molds, as taught by Sorensen in U.S. Pat. No. 4,971,747. Sorensen teaches the use of a reciprocal stacked 4-level molding system having an asymmetrical stock flow path feeding the respective "left" and "right" sides of the mold stack (relative to the mold centreline), with plastic material being injected first to one of the sides of the stack, and, after that side has set-up, opening the mold interface to eject the contents of the respective cavities while closing another mold interface and injecting stock into the other side of the stack.
In Sorensen (U.S. Pat. No. 4,971,747) as in certain of the below listed prior art patents, numerous stock flow control valves are shown, in Sorensen's multirunner stock feed. These stock system flow control valves may be used, among other things, for the purpose of preventing the drool of liquid stock into the immediate zone of the mold interfaces. The occurrence of such drooling is most disadvantageous to the operation of any type of mold, and can lead to significant spoilage losses of finished product, and/or mold damage, while also causing cycle interruption and consequent loss of production. Sorensen also uses a snorkel of fixed stroke, which may lead both to stock spillage and air entrainment in its operation.
The illustrative prior art patents are as follows:
______________________________________ U.S. PAT. NO. ISSUE DATE INVENTOR ______________________________________ 2,770,011 November 1956 Vely 3,533,594 October 1970 Segmuler 3,806,295 April 1974 Gellert 3,843,294 October 1974 Bielfeldt et al. 3,934,626 January 1976 Hall 4,207,051 June 1980 Wright et al. 4,212,626 July 1980 Gellert 4,309,163 January 1982 Cottancin 4,473,347 September 1984 Terashima 4,477,242 October 1984 Eichlseder et al. 4,586,887 May 1986 Gellert 4,599,064 July 1986 Landis et al. 4,663,811 May 1987 Gellert 4,669,971 June 1987 Gellert 4,971,747 November 1990 Sorensen ______________________________________ JAPANESE PATENT NO. INVENTOR ______________________________________ 51-102 047 Kokai ______________________________________
The Japanese Kokai 51-102 047 shows in one embodiment an injection nozzle located external to the press and located upon the mold centre axis. The axial single expansion of the one-piece nozzle construction is spring-driven, to a fixed, full stroke, with no regard to resultant internal stock pressure, which can become less than atmospheric, such that air induction is possible. The spring loading of the nozzle is added to the clamping tonnage force. Adjustments may be applied thereto externally of the press, with virtually no limitation upon accessability or available space. Any variations in nozzle geometry due to changing thermal conditions can be accommodated by compensatory displacement of the press injection nozzle. The arrangement is located symmetrically on the mold axis, and is entirely insensitive, with no unbalancing effect on mold opening and closing.
In a second embodiment the one-piece nozzle arrangement is shown to provide direct injection, into a mold cavity, and comprises a symmetrical, off-centre nozzle which does not separate from the back of the mold into which it is injecting.